1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a method of driving a plasma display panel that is adaptive for improving brightness and efficiency.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, since a three-electrode, alternating current (AC) surface-discharge PDP lowers a voltage required for a discharge by utilizing wall charges accumulated in the surface thereof upon discharge and protects electrodes from a sputtering generated by the discharge, it has advantages of a low-voltage driving and a long life.
Referring to FIG. 1, a conventional three-electrode, AC surface-discharge PDP includes a scanning electrode Y and a sustaining electrode Z provided on an upper substrate 10, and a data electrode X provided on a lower substrate 18.
The scanning electrode Y and the sustaining electrode Z have transparent electrodes 12Y and 12Z with a large width and metal bus electrodes 13Y and 13Z with a small width, respectively, and are formed on the upper substrate in parallel. An upper dielectric layer 14 and a protective film 16 are disposed on the upper substrate 10 in such a manner to cover the scanning electrode Y and the sustaining electrode Z. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer 14. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO). The data electrode X is perpendicular to the scanning electrode Y and the sustaining electrode Z.
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a fluorescent material layer 26. The barrier ribs 24 separate adjacent discharge spaces in the horizontal direction to thereby prevent optical and electrical crosstalk between adjacent discharge cells. The fluorescent layer 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive mixture gas of He+Xe or Ne+Xe is injected into a discharge space defined between the upper and lower substrate 10 and 18 and the barrier rib 24.
Discharge cells of the three-electrode PDP are arranged at a panel 30 in a matrix pattern as shown in FIG. 2. The scanning electrodes Y1 to Ym and the sustaining electrodes Z1 to Zm arranged in parallel cross the data electrodes X1 to Xn at each discharge cell.
Such a PDP drives one frame, which is divided into various sub-fields having a different discharge frequency, so as to realize gray levels of a picture. Each sub-field is again divided into a reset interval for uniformly causing a discharge, an address interval for selecting the discharge cell and a sustaining interval for realizing the gray levels depending on the discharge frequency.
For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to 1/60 second (i.e. 16.67 msec) is divided into 8 sub-fields SF1 to SF8 as shown in FIG. 3. Each of the 8 sub-fields SF1 to SF8 is again divided into a reset interval, an address interval and a sustaining interval. The reset interval and the address interval of each sub-field are equal every sub-field. The address discharge for selecting the cell is caused by a voltage difference between the data electrode X and the scanning electrode Y. The sustaining interval is increased at a ration of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field. A sustaining discharge frequency in the sustaining interval is controlled at each sub-field in this manner, to thereby realize a gray scale required for a picture display. The sustaining discharge is generated by a high voltage of pulse signal applied alternately to the scanning electrode Y and a sustaining electrode Z.
FIG. 4 illustrates driving waveforms of the three-electrode PDP.
Referring to FIG. 4, in the reset interval, a reset discharge for initializing the discharge cell is generated by a reset pulse Vr applied to the sustaining electrode Z. Such a reset pulse Vr may be applied to the scanning electrode Y. At this time, a positive pulse signal with a low voltage level is applied to the data electrode X so as to prevent an erroneous discharge from being generated between the sustaining electrode Z and the data electrode X.
In the address interval, a scanning pulse −Vsc is sequentially applied to the scanning electrode Y and a data pulse Vd synchronized with the scanning pulse −Vsc is applied to the data electrode X. An address discharge is generated at the discharge cell supplied with the data pulse Vd. A low-level positive direct current (DC) voltage is applied to the sustaining electrode Z so as to prevent an erroneous discharge from being generated between the data electrode X and the sustaining electrode Z.
In the sustaining interval, a sustaining pulse Vs are alternately applied to the scanning electrode Y and the sustaining electrode Z. Then, the discharge cells selected by the address discharge generates a sustaining discharge continuously whenever the sustaining pulse Vs is applied.
Since such a three-electrode PDP has the scanning electrode Y and the sustaining electrode Z positioned at the upper center of the discharge space, it has a low utility of the discharge space. For this reason, in the three-electrode PDP, a voltage for causing a sustaining discharge and a power consumption are high while discharge and light-emission efficiencies during the sustaining discharge are low. More specifically, the sustaining discharge takes a surface discharge between the scanning electrode Y and the sustaining electrode Z. However, since the scanning electrode Y and the sustaining electrode Z concentrate at the center of the cell to lower a discharge-initiating voltage, a discharge path becomes short to cause low discharge and light-emission efficiencies. When a distance between the scanning electrode Y and the sustaining electrode is enlarged so as to enhance the efficiencies, a discharge-initiating voltage becomes high in proportional to a distance between the two electrodes. Furthermore, when an electrode width of at least one of the scanning electrode Y and the sustaining electrode Z is widened so as to enhance an efficiency, power consumption rises due to an increase in discharge current.
In order to solve the problems of the three-electrode PDP, there has been suggested a five-electrode PDP in which an electrode for causing a sustaining discharge is divided into four electrodes.
Referring to FIG. 5, the conventional five-electrode PDP includes first and second trigger electrodes TY and TZ provided on an upper substrate 34 in such a manner to be positioned at the center of a discharge cell, first and second sustaining electrodes SY and SZ provided on the upper substrate 34 in such a manner to be positioned at the edge of the discharge cell, and a data electrode X provided at a lower substrate 40 in such a manner to be perpendicular to the trigger electrodes TY and TZ and the sustaining electrodes SY and SZ.
The trigger electrodes TY and TZ and the sustaining electrodes SY and SZ include transparent electrodes having a large width and metal bus electrodes having a small width, respectively, and are formed on the upper substrate 34 in parallel. The trigger electrodes TY and TZ can be easily discharged at a low potential difference because a distance Ni between the electrodes is small. The first trigger electrode TY also plays a role to cause an address discharge by a voltage level difference between an applied scanning pulse and a data pulse applied to the data electrode X. The sustaining electrodes SY and SZ are set to have a large distance Wi between the electrodes with having the trigger electrodes TY and YZ therebetween. The sustaining electrodes SY and SZ causes a long-path discharge by utilizing space charges and wall charges formed by a discharge between the trigger electrodes TY and TZ.
An upper dielectric layer 36 and a protective film 38 are disposed on the upper substrate 34 in such a manner to cover the trigger electrodes TY and TZ and the sustaining electrodes SY and SZ. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer 36. The protective film 38 prevents a damage of the upper dielectric layer 36 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 38 is usually made from magnesium oxide (MgO).
A lower dielectric layer 44 and barrier ribs 46 are formed on the lower substrate 40. The surfaces of the lower dielectric layer 44 and the barrier ribs 46 are coated with a fluorescent material layer 48. The barrier ribs 46 separate adjacent discharge spaces in the horizontal direction to thereby prevent optical and electrical crosstalk between adjacent discharge cells. The fluorescent material layer 48 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive mixture gas of He+Xe or Ne+Xe is injected into a discharge space defined among the upper and lower substrate 34 and 40 and the barrier ribs 46.
Discharge cells of the five-electrode PDP are arranged at a panel 60 in a matrix pattern as shown in FIG. 6. Pairs of the scanning electrodes TY1 to TYm and TZ1 to TZm and pairs of the sustaining electrodes SY1 to SYm and SZ1 to SZm arranged in parallel cross the data electrodes X1 to Xn at each discharge cell.
Like the three-electrode PDP, such a five-electrode AC surface-discharge PDP drives one frame, which is divided into various sub-fields having a different discharge frequency, so as to realize gray levels of a picture.
FIG. 7 shows driving waveforms of the five-electrode PDP.
Referring to FIG. 7, in the reset interval, a positive reset pulse Vrst having a high voltage level is applied to the second trigger electrode TZ. Then, the discharge cells at the entire field are reset-discharged to left a constant quantity of wall charges at the discharge cells a the entire field. At this time, a positive pulse signal with a low voltage level is applied to the data electrode X so as to prevent an erroneous discharge from being generated between the second trigger electrode TZ and the data electrode X.
In the address interval, a scanning pulse −Vsc is sequentially applied to the first trigger electrodes TY. A data pulse Vd synchronized with the scanning pulse −Vsc is simultaneously applied to the data electrodes X. The discharge cell supplied with the data pulse Va causes an address discharge by a voltage difference between the data electrode X and the first trigger electrode TY and an internal wall voltage.
In the sustaining interval, a trigger pulse Vt and a sustaining pulse Vs are simultaneously applied to the first trigger electrode TY and the first sustaining electrode SY, respectively. Also, the trigger pulse Vt and the sustaining pulse Vs are simultaneously applied to the second trigger electrode TZ and the second sustaining electrode SZ, respectively. Herein, a voltage level of the trigger pulse Vt is set to be lower than that of the sustaining pulse Vs. When a first trigger pulse Vt is applied to the first trigger electrode TY, the discharge cells having generated the address discharge cause a short-path discharge between the first trigger electrode TY and the second trigger electrode TZ. By this short-path discharge, space charges and wall charges are created within the discharge cells selected by the address discharge. The space charges and the wall charges created by the short-path discharge provide a priming effect with respect to a long-path discharge between the first and second sustaining electrodes SY and SZ. In other words, the priming effect caused by the short-path discharge induces a long-path discharge between the first and second electrodes SY and SZ. In other words, the short-path discharge between the trigger electrodes TY and TZ can cause a long-path discharge between the sustaining electrodes SY and SZ having a wide distance between electrodes at a low voltage.
The sustaining discharge process in the five-electrode PDP is as shown in FIG. 8A and FIG. 8B.
Referring to FIG. 8A and FIG. 8B, if a trigger pulse Vt is applied to the first trigger electrode TY, then a short-path discharge is generated between the first trigger electrode TY and the second trigger electrode TZ. Subsequently, when a sustaining pulse Vs synchronized with the trigger pulse Vt is applied to the first sustaining electrode SY, a discharge occurs between the first trigger electrode TY and the first sustaining electrode SY as shown in FIG. 8A with the aid of wall charges and space charges created upon discharge between the first trigger electrode TY and the second trigger electrode TZ. Likewise, when a sustaining pulse Vs synchronized with the trigger pulse Vt is applied to the second sustaining electrode SZ, a discharge occurs between the second trigger electrode TZ and the second sustaining electrode SZ as shown in FIG. 8B with the aid of wall charges and space charges created upon discharge between the first trigger electrode TY and the second trigger electrode TZ. When the wall charges and the space charges created by the discharge between the first trigger electrode TY and the first sustaining electrode SY (or the discharge between the second trigger electrode TZ and the second sustaining electrode SZ) is added to a sustaining pulse Vs applied from the exterior to generate a voltage difference enough to cause a long-path discharge, a long-path discharge occurs between the first sustaining electrode SY and the second sustaining electrode SZ.
Herein, the long-path discharge between the first and second sustaining electrodes SY and SZ only contributes to brightness. The discharge between the trigger electrodes TY and TZ or the short-path discharge between any one trigger electrode TY or TZ and any one sustaining electrode SY or SZ are priming discharges for creating charged particles permitting a long-path discharge.
In the conventional five-electrode PDP, the discharge between the trigger electrodes TY and TZ spaced at a narrow distance Ni or the short-path discharge between any one trigger electrode TY or TZ and any one sustaining electrode SY or SZ should be weakly generated for the purpose of obtaining a stable long-path discharge. Also, in the conventional five-electrode PDP, since most wall charges created by the address discharge concentrates on the first trigger electrode TY, the discharge between the trigger electrodes TY and TZ during the sustaining discharge is relatively strongly generated while the long-path discharge between the sustaining electrodes SY and SZ is weakly generated.
An experimental result shows that the discharge between any one trigger electrode TY or TZ and any one sustaining electrode SY or SZ weakens the long-path discharge between the sustaining electrodes SY and SZ to cause a deterioration of brightness. Accordingly, there has been required a scheme capable of weakening or eliminating the discharges between the trigger electrode TY or TZ and the sustaining electrodes SY and SZ causing a deterioration of brightness.